Bull. Natn. Sci. Mus., Tokyo, Ser. A, 31(2), pp. 45–50, June 22, 2005

A New Spider of the Genus Achaeus (Crustacea, , Brachyura) from the Kermadec Islands

Richard Webber1 and Masatsune Takeda2

1 Museum of New Zealand Te Papa Tongarewa PO Box 467, Wellington, New Zealand e-mail: [email protected] 2 Department of Zoology, National Science Museum, Tokyo 3–23–1 Hyakunincho, Shinjuku-ku, Tokyo, 169–0073 Japan e-mail: [email protected]

Abstract A new species of crab in the genus Achaeus (Crustacea, Decapoda, Brachyura, Inachi- dae) is described from a male holotype collected at the Kermadec Islands in the South Pacific. The species, named A. kermadecensis, is noticeably small in size among its congeners and most unusu- al in having very strong gastric and cardiac protuberances. Key words: Achaeus, , spider crab, new species, Kermadec Islands, New Zealand, South Pacific.

While examining in the collections of mm; carapace width, across branchial regions of the Museum of New Zealand Te Papa Tongare- both sides, 3.36 mm), R.V. Acheron Bottom Sta- wa, from the Kermadec Islands, northwest of tion 307, Kermadec Islands, Raoul Island, be- New Zealand in the South Pacific, we encoun- tween Meteorological Station and Hutchinson tered a very small male of a unique spider crab Bluff, 4 April 1973, 146–110 m, beam trawl. belonging to the family Inachidae. In spite of its Description. Carapace (Figs. 1a, b, 2a, b) small size, the first pleopod is particularly well elongate-pear-shaped, length 1.42 times of great- developed; a distinctive specific character togeth- est width; median hepatic region drawn to a tall, er with exceptionally strong and tall gastric and peak-like protuberance, cardiac region encom- cardiac protuberances. Examination of the litera- passed by and produced into a similarly tall, ture indicated that this sole specimen represents a broad-based, posteriorly biased protuberance, new species in the genus Achaeus Leach, 1817, carapace otherwise without prominent protuber- which is composed of no less than 27 Indo-West ances. Dorsal and lateral surfaces more or less Pacific species (Griffin & Tranter, 1984) and 7 completely covered by unevenly sized, mostly East Atlantic species (Manning & Holthuis, round-topped tiny tubercles, lowest and spaced 1981). out in flattened area between hepatic and cardiac In the following account we describe the new protuberances, virtually absent in grooves behind species under the name Achaeus kermadecensis, hepatic regions and on branchial regions lateral after the type locality. to cardiac protuberance. Rostrum curving downwards anteriorly to house antennular fossa, rostral lobes blunt, un- Achaeus kermadecensis sp. nov. evenly tuberculate, separated by a notch with a (Figs. 1–3) shallow groove posterior to notch narrowing pos- Material examined. One male, holotype teriorly, closing at level of eyes. Supraorbital (NMNZ CR. 10009) (carapace length, from tip eave flared, arching over eye, roughened dorsally of rostrum to posterior margin of carapace, 4.78 and at edges by uneven, sometimes elongate tiny 46 Richard Webber and Masatsune Takeda

Fig. 1. Achaeus kermadecensis sp. nov., holotype, ? (NMNZ CR. 10009; 4.78 mm in carapace length and 3.36 mm in carapace width), dorsal (a, b) and ventral (c) views. tubercles. Eyestalks short, stout (right eyestalk with an almost vertical groove above the con- twisted back in holotype), a prominent tubercle striction running up behind protogastric region, protruding dorsally from eye (Fig. 2a, b), a sec- more or less lacking tiny tubercles, petering out ond small tubercle near eye on anterior surface of short of midline. Anteromedial part of branchial eyestalk, a third small tubercle between eye and regions behind almost vertical groove, raised midpoint on posterior surface of eyestalk (Fig. to a low, tuberculate hummock, posteromedial 2c). branchial regions lateral to intestinal region also Region between eyes and hepatic region con- vaguely hummocked; branchial regions expanded stricted, cuticle smooth ventrolaterally, a horizon- laterally, only slightly inflated. tal, unevenly tuberculate prominence in proto- A few, very small, straight hairs scattered gastric region produced behind eye, extending among tubercles on branchial region, carapace posteriorly above hepatic regions. Hepatic regions otherwise lacking hairs. inflated, with a tubercle anterolaterally in ptery- Antennular fossa (Fig. 2c) elongate oval, thin- gostomian area of inflation almost overwhelmed lipped, edges roughened by tubercles, smooth by uneven, tiny tubercles. internally; basal segment of each antennule Carapace constricted behind hepatic inflations, roughened by tiny tubercles over whole anterior New Spider Crab from the Kermadec Islands 47

Fig. 2. Achaeus kermadecensis sp. nov., holotype, ? (NMNZ CR. 10009). a, carapace, dorsal view (antennal fla- gella not shown); b, carapace, lateral view; c, front, ventral view; d, thoracic sternum between cheliped coxae, ventral view; e, abdomen, posterior (dorsal) view. (Scales1 mm). 48 Richard Webber and Masatsune Takeda surface, antennular partition drawn downwards two thirds of depression bordered by small into a blunt-tipped blade (Fig. 2b), roughened by spines, about three near joint with basis, a lateral low-set tiny tubercles on edges and submarginal- submarginal row of five, two tiny blunt spines ly. proximally on lateral margin, a single tiny spine Thoracic sternum between cheliped coxae at distolateral corner of ischium, three small (Fig. 2d) with, in anterior half, an oval depression spines along distal margin adjacent to joint with either side of a low, flat-topped, forwardly direct- merus, eight to nine small spines in an uneven ed fin-like spine, a small, sharp spine posterior to row median to shallow depression, a scattering of fin-like spine at base of posterior half of sternum at least 12 additional tiny, blunt tubercles be- which rises steeply to edge of abdominal fossa; tween this row and median margin of ischium, edge of deep abdominal fossa armed with close- median margin with seven small, well spaced set, unevenly sized and distributed tubercles. teeth (a double-sized space between distal two Abdomen (Figs. 1c, 2e) with first to fifth seg- and proximal five teeth); merus with lateral mar- ments short, much wider than long, sixth (final) gin slightly produced distally, bordered by six segment slightly wider than long, third and well spaced, very small spines, shallow longitudi- fourth together convex laterally, third widest, to- nal groove on external surface one third from gether wider than remainder, borders of sixth median margin, rising medially to support sub- slightly convex anteriorly, distal margin evenly marginal row of robust, sharp spines, proximal rounded; third and fourth segments combine to four small, fifth long, sixth very long, seventh form a round bulge either side of midline (visible short, broad-based, near joint with carpus (palp); as cup-like hollows on ventral surface of ab- carpus with a small, inconspicuous spine distally domen), an area of blunt, tiny tubercles laterally on medial margin; propodus with two tiny spines on third; first segment drawn into an inconspicu- in similar position to carpal spine; dactylus with- ous median tubercle, second to fifth segments out spines. Ischium with numerous fine hairs on each with a more prominent median tubercle, medial margin and submarginally on anterior and tallest on fifth segment; sixth with a short median posterior surfaces, merus with a denser patch of ridge in anterior half rising posteriorly to a small, hairs submarginally on anterior surface, three bluntly pointed spine, raised area in posterior half segments of palp armed with similar patches of of sixth segment encompassing a pair of shallow, dense, long, hairs on distal, anterior surfaces (on longitudinal pits adjacent to midline. carpus overlapping those of propodus, on pro- Basal antennal articles (Fig. 2b, c) with a podus overlapping those of dactylus) to form strong ventral spine one third from distal margin continuous, distally directed ‘brush’ of hairs; with, anterior and posterior to it, about 15–20 remaining endopod surfaces with very few hairs. smaller, unevenly sized and spaced tubercles ven- Exopod with about three tiny blunt tubercles trally and ventrolaterally, smallest most proximal posteriorly near base, a small, inconspicuous where article becomes continuous with epistome. flagellum originating subterminally, lateral edge Antennal flagellum (Fig. 2b) fine, short, little of exopod with hairs spaced along two thirds of more than one quarter length of carapace, of length with a few submarginal. seven–eight segments, bearing a few very fine Chelipeds (Figs. 1, 3c, d) more robust than hairs. Epistome of similar length and breadth, a ambulatory legs but not swollen, about half tiny tubercle anterior to green gland opening on length of carapace; merus (not illustrated) with a left side only, cuticular surface otherwise smooth. dorsolateral, longitudinal row of small, blunt Ischium of third maxilliped endopod with spines, a second uneven, longitudinal row of dished anterior surface (Fig. 3a), posterior (exter- larger tubercles ventrolaterally; carpus (Fig. 3c) nal) surface (Fig. 3b) with a slight median, longi- with several small, blunt, and one larger spine tudinal, shallow, unarmed depression; posterior dorsomedially, an interrupted row of tubercles di- New Spider Crab from the Kermadec Islands 49

Fig. 3. Achaeus kermadecensis sp. nov., holotype, ? (NMNZ CR. 10009). a, b, left third maxilliped, anterior (inner) (a) and posterior (b) views; c, carpus of right cheliped, dorsal view; d, right chela, lateral view; e, fourth ambulatory leg left side, posterior view; f, dactylus of fourth ambulatory leg, left side; g, h, right first pleopod, abdominal (g) and sternal (h) views. (Scales. a, b, and g, h0.5 mm; c, d, f, and e1 mm). agonally from dorsal hinge with chela towards small tubercles dorsally, dorsolaterally, ventrolat- lateral hinge with merus, proximal spine much erally, ventrally; fingers half length of chela, gap- larger than other spines in row; chela (Fig. 3d) ing very narrowly in proximal two thirds, a few slightly compressed, fingers curving medially, ventral tubercles on proximal half of fixed finger; palm twice as long as high with inconspicuous cutting edge of fixed finger with nine, unevenly 50 Richard Webber and Masatsune Takeda distributed, low-profile teeth, of movable finger colour apparent. with eight such teeth, otherwise fingers unarmed, Remarks. The triangular shape of the postor- chela with very few hairs, most occurring dorsal- bital carapace is not much different from that of ly and laterally on movable finger. the typical Achaeus species, but the tall gastric Ambulatory legs (Fig. 1a) long and slender, and cardiac tubercles are characteristic of this first longest, approximately 2.7 times length of species. In some species the cardiac region may carapace; second to fourth (last) decreasing in be more or less raised and tipped with one or two size, fourth (Fig. 3e) approximately 1.8 times papillate small tubercles, but neither tall nor length of carapace. First to third legs with a few densely tuberculated as in this species. In A. ker- curled hairs singly and in groups dorsally on madecensis the gastric tubercle is considerably meri, carpi and propodi, curled hairs on merus less broad-based or robust than the cardiac tuber- and carpus of fourth leg (Fig. 3e), straight hairs cle, but the gastric tubercle is at least as tall as on legs, scattered on dorsal surfaces and most the cardiac tubercle and of similar shape in pro- numerous ventrally on propodi; dactylus of first file, which also distinguishes this species from all ambulatory leg nearly straight for most of length, others in the genus. curved near tip, those of second to fourth legs (Fig. 3f) progressively more curved, dactyli of all Acknowledgements ambulatory legs each with a single straight or slightly hooked spine ventrally adjacent to darkly We are grateful to the authorities of the Muse- pigmented tip of each dactylus, distal to this um of New Zealand Te Papa Tongarewa and the spine a slight swelling bearing minute hairs, National Science Museum, Tokyo, for the oppor- proximal to this spine a ventral row of strong, ar- tunity for Masatsune Takeda to visit Te Papa and ticulated, plumose setae in distal half to two Richard Webber to visit the National Science thirds of dactylus. Museum. First pleopod (Fig. 3g, h) large and robust, dis- tinctly curved around mid length, tip rounded, References aperture partly shielded by cuticle of rounded tip, abdominal edge of aperture with a row of tiny Griffin, D. J. G. & H. A. Tranter, 1986. The Decapoda Brachyura of the Siboga Expedition. Part VIII. Maji- hairs, a gathering of minute hairs about lateral dae. Siboga-Exp., 39 (C4): 1–335. edge of aperture, abdominal surface of pleopod Manning, R. B. & L. B. Holthuis, 1981. West African with scattered tiny hairs mainly in distal half, brachyuran crabs (Crustacea: Decapoda). Smiths. otherwise naked. Contr. Zool., (306): i–xii1–379. Colour. preserved in ethanol with no